Observations from UVM Field Naturalists and Ecological Planners

Tag Archives: dolostone

I’m not a geologist, but recently I learned a thing or two about Vermont bedrock that bumps it above maple syrup or cheese on Vermont’s “Best of” List.

By nature, I ask a lot of questions: What trees are those? How deep is this soil? What bird lives in that nest? Turns out, a lot of the answers are directly or indirectly related to the kind of rock below. And in Vermont, those are calcium-rich rocks—which create an alluring hotspot for many cool, rare or economically important plants.

Picture Vermont 500 million years ago, covered by a vast ocean full of planktonic organisms—a primordial soup. Over time, generations of these tiny organisms died and their bodies drifted to the seafloor laying down sediment full of calcium. When the land shifted and the ocean receded, these compressed sediments formed the basis for the calcareous bedrock of today’s Champlain Valley, mostly dolostone.

So what’s the deal with calcium? Plants need it for metabolism and structure, just like we do. It also helps to raise the pH of the soil (thus lowering the acidity). The chemistry gets a little complicated—but find enlightenment (like I did) in a bottle of Tums. Calcium carbonate, well-known for soothing heartburn, also neutralizes acidity in soil making it more alkaline. Who cares? Bacteria, for starters. And those rascals are necessary for making nitrogen available to plants. In fact, under acidic conditions many nutrients give plants the cold shoulder—instead they’re hooking up with each other or leaching out of plants’ reach. Where dolostone (or limestone) is close to the surface (thanks to several glaciations and years of other erosive processes) these nutrients are more willing.

Farmers have known this forever and call neutral or alkaline soils “sweet.” Plant biologists know it too. I’m embarrassed to admit it took nearly a semester of botany for me to pick up on the pattern of our field trip locations—calcareous bedrock stared me straight in the eye.

Maidenhair fern near Gleason Brook (photo courtesy of Ryan Morra)

For instance, check out the Long Trail near Gleason Brook in Bolton, VT. If you park in the lot off of Duxbury Rd. and hike up a quarter mile or so, you will start to see telltale plants of calcium-enriched soils like maidenhair fern, wood nettle, blue cohosh, plantain-leaved sedge and white baneberry (doll’s eyes). Sugar maple, white ash, basswood and hophornbeam dominate the tree canopy while striped maples sit eagerly in the understory. Stay on the trail to find the dense patch of pale touch-me- not, an irregular pale yellow flower, at the base of a steep slope on the south side of the trail. Here the downward movement of soil and nutrients from the upper slope along with the exposed calcareous bedrock create a double whammy of plant nutrient bliss. Scientists describe this type of vegetative community as a Rich Northern Hardwood Forest—sounds fancy but Vermonters are spoiled with this natural community-type in ample abundance.

Wood nettle near Gleason Brook (photo courtesy of Ryan Morra)

Vermont’s best-kept secret, dolostone, has broader implications than satisfying curious botanizers. Conservation planners, for instance, can use geologic surveys to identify potential priority areas for rare plants among Vermont’s varying bedrock landscape. If you travel a few miles farther on the Long Trail up toward the summit of Camel’s Hump your heartburn might return—the rock transitions to more resistant igneous and metamorphic rocks resembling the bedrock geology of our neighbors to the east in “The Granite State.” At the summit’s rare (seemingly masochistic) alpine plants thrive under harsh, acidic conditions—yet another botanical treat thanks to the state’s multifarious geologic past. Motley geology begets vegetative diversity.

So, next time you douse your pancakes with maple syrupy goodness, take a moment to thank the nutrient-rich soil conditions integral to the Sugar maple-dominated forest community of Vermont.